Method for making a quasi-incompressible phase-change material, shear-thinned and with low heat conductivity

ABSTRACT

The process according to the invention includes the combination, with a liquid phase change material (PCM), of a texturing agent chosen so as to greatly reduce the thermal convection and whose viscosity is decreased reversibly under shearing. The material formed has a gelled consistency when at rest, and fluidized under shearing. The PCM comprises a mixture of chemical compounds from the alkane family: paraffins, waxes, fatty alcohols, fatty acids etc., and the texturing agent is a high mass polymer (hydrocarbonate polymers, ester or ether polymers, mixed ester-hydrocarbon polymers), an ionomer polymer or a di, tri or multi-block styrene copolymer (SBS: styrene-butadiene-styrene, SEBS: styrene-ethylene-butadiene-styrene).  
     Applications : thermal insulation of vessels or lines, and more especially, for hydrocarbon transport lines.

FIELD OF THE INVENTION

[0001] The present invention concerns a process for manufacturing amaterial based on phase change materials (PCM), quasi-incompressible andhaving low thermal conductivity, and the product obtained by the processand the applications. The material has the characteristic of being ableto be fluidized by shearing, then to gel at rest.

[0002] The material according to the invention can be used as thermalinsulant in many areas, in particular for the thermal insulation oflines or pipes carrying fluids likely to major changes of state underthe influence of temperature: crystallisation of paraffins, depositionof hydrates, ice, etc.

[0003] This is for example the case in the field of hydrocarbonproduction. In many cases, it is necessary to provide submarine lineswith thermal insulation to keep the fluids flowing, and to prevent foras long as possible, the formation of hydrates or paraffin orasphaltene-rich deposits. Deep sea developments often accumulate thesedrawbacks which are particularly detrimental in the event of productionstoppages.

BACKGROUND OF THE INVENTION

[0004] Various heat insulation techniques are described, for instance,in the following documents: FR 98/16.791, JP 2 176 299, or WP 97/47174.

[0005] Heat insulation can be accomplished by a variety of processes. Onshore, or at shallow depths, cellular or wool-type porous cellularmaterials are used, to stop the convection of low thermal conductivitygas. The compressibility of these porous materials prohibits thetechnique from being used at relatively great depths.

[0006] Another known technique consists in wrapping the line with afirst coat of porous material soaked in paraffin, for instance, whosethermal insulation coefficient is lower than those obtained with the gastrapping technique mentioned above, and a second coat of refractorymaterial strengthening the effect of the first coat. However, this kindof solution cannot be used in water.

[0007] There are other solutions that are more suitable for use at greatdepths. For instance, it is possible to use:

[0008] solid quasi-incompressible polymer material coatings based onpolyurethane, polyethylene, polypropylene etc. which, however, offerrelatively average thermal conductivity, insufficient to avoid drawbacksin the event of production stoppages;

[0009] coatings of syntactic materials comprising hollow ballscontaining a gas and resisting the outside pressure, immersed in binderssuch as concrete, epoxy resin etc., whose conductivity is lower thanthat of the compact materials, but that are far more costly.

[0010] It is also possible to protect the line in which the fluidscirculate by an outer line withstanding the hydrostatic pressure. A heatinsulation with low thermal conductivity left at atmospheric pressure orplaced under vacuum, with partitions placed at regular intervals forsafety reasons, is for example interposed in the annulus between them.

[0011] It is also well-known to interpose between the line and adeformable protective sheath an absorbing matrix enclosing the line,impregnated with a liquid/solid phase change quasi-incompressiblematerial having a melting temperature higher than that of thesurrounding environment and lower than that of the fluids circulatingthrough the line.

[0012] The phase change materials (PCM) behave like heat accumulators.They release this energy in the course of solidification(crystallisation) or absorb this energy during fusion, in a reversiblemanner. These materials can therefore be used to increase the length ofproduction stoppages without any risks of the lines being clogged bypremature cooling of their content.

[0013] Known examples of phase change materials are chemical compoundsof the alkanes family C_(n)H_(2n+2), such as for instance, n-paraffins(C₁₂ to C₆₀), which represent a good compromise between the thermal andthermodynamic properties (fusion temperature, latent fusion heat,thermal conductivity, calorific capacity) and cost. These compounds arethermally stable in the range of operating temperatures considered andare compatible with use in the marine environment because they areinsoluble in water and have a very low toxicity level. Therefore, theyare well suited to the thermal insulation of deep water lines.

[0014] The change of state temperature of these phase change materialsis related to the carbon number of the hydrocarbon chain and cantherefore be adapted to a particular application. To obtain a phasechange at around 30° C., it is possible, for instance, to use a mixtureof paraffins essentially comprising C₁₈ such as Linpar 18-20 marketed byCONDEA Augusta S.p.A.

[0015] The use of waxes, normal paraffins, long-chain weakly branchedisoparaffins (C₃₀-C₄₀) (1 or 2 branches), of long chain branchedalkylcycloalkanes or long chain branched alkyl aromatics, also weaklybranched, fatty alcohols or fatty acids, may also be considered.

[0016] Above their fusion temperature Tf, phase change materials (PCM)are in the liquid phase and their viscosity is low. To overcome thisdrawback, which is particularly inconvenient for some applications,particularly in the manufacturing of double wall vessels, or energystorage drums, it is well-known to add a thickening agent, such assilica, to solidify them and prevent leaks from occurring.

[0017] Another drawback of phase change materials (PCM) is that theirliquid state favours thermal losses by convection.

SUMMARY OF THE INVENTION

[0018] The process according to the invention allows to manufacture amaterial or product based on quasi-incompressible phase change material(PCM) having low thermal conductivity at a temperature higher than theirfusion temperature Tf and fluidized under shearing.

[0019] It includes the combination, with a phase change material, of atexturing agent chosen so as to very considerably reduce the thermalconvection at a temperature higher than the fusion temperature of thephase change material.

[0020] The texturing agent is brought into solution in the PCMconsidered in such a way as to give the phase change material a gel-likeconsistency once the material is at rest. The texturing agent is chosento obtain fluidification under shearing. In this way, the flow of thematerial through a tank or a line can take place more easily, inparticular by pumping or pouring.

[0021] Once in place, the texturing agent gels the material at the pointwhere its primary function of thermal insulant is required.

[0022] If necessary, the product may contain anti-oxidant oranti-bacterial agents, corrosion inhibitors or an insoluble fillerdesigned to adjust its density or its thermal conductivity, additivesdesigned to improve its stability or a solvent designed to control itsviscosity.

[0023] The product according to the invention can be used for thermalinsulation in general. In particular, it can be applied to the thermalinsulation of lines transporting hydrocarbons, where it may be used as adirect or interposed coating (injected) between the lines and an outerprotective sheath.

[0024] Other characteristics and advantages of the process and of thematerial produced according to the invention, together with severalapplication examples, are described hereafter.

DETAILED DESCRIPTION

[0025] The manufacturing process as described here consists in bringinginto solution, in a phase change material (hereinafter referred to asPCM), a texturing agent chosen to increase the viscosity of the PCM anddecrease the thermal convection of the PCM in the liquid state so as toform an insulating blocked convection substance having a gelledconsistency at rest, and is fluidized under shearing.

[0026] The liquid component forming the continuous phase can be amixture of chemical compounds from the family of alkanes C_(n)H₂₊₂ suchas, for instance, paraffins (C₁₂ to C₆₀) or waxes, normal paraffins,long chain isoparaffins (C₃₀-C₄₀), very weakly branched (1 or 2branches), long chain branched alkylcycloalkanes or long chain branchedalkylaromatics, fatty alcohols or fatty acids. The liquid componentrepresents between 60% and 99.99% of the product mass, while thecomplement is the texturing agent.

[0027] The texturing agent is:

[0028] a high mass polymer (weight average molecular weight around 25000to 2 million g/mole): hydrocarbonate polymers, ester or ether polymersor mixed polymers;

[0029] a charged polymer and/or ionomer polymers. Ionomer polymers aremacromolecules having a molecular mass included between 1000 and 5million, preferably between 20000 and 1 million g/mole, containing asmall percentage of ionic groups (included between 0.005% and 10% bymole, preferably between 0.01% and 5% and even more preferably between0.2% and 3%) chemically linked and distributed along the non-ionicpolymer chains. These polymers are obtained:

[0030] either by co-polymerisation between a functionalized monomer anda hydrophobic monomer such as an olefin (for instance: acrylic acid ormethacrylic acid with ethylene).

[0031] or by the modification of a preformed low polarity polymer (e.g.,controlled sulfonation of polystyrene).

[0032] a styrene block co polymer, preferably hydrogenated. Blockcopolymers are thermoplastic elastomers in which polymer chains have adi-block, tri-block, or multi-block configuration. Tri-block copolymershave polystyrene segments (S) at the end of the molecule (preferablyclose to 30% by mass) and an elastomer segment at the centre. Thedi-block molecule simply has a polystyrene segment attached to anelastomer segment.

[0033] The configuration and the molecular mass vary with the grade ofthe copolymer (the molecular mass of polystyrene will preferentially beincluded between 5000 and 30000 g/mol and that of elastomer will bearound 5000 g/mol).

[0034] The strong interactions between the high-mass polymer and the PCMwill allow the penetration of the PCM molecules into the polymermacromolecules. The latter have very large dimensions in solution, theyintermingle while slowing down the flow of the PCM layers to which theybelong, causing an increase in the composition viscosity.

[0035] In the case of charged non-polar polymers, the ionic groupsdistributed along the chains form, by an association of intermolecularion pairs, ion-rich aggregates. The aggregates thus formed consequentlyincrease, in the semi-dilute state, the viscosity of the solutioncompared to the same polymer, not charged, with an equivalent molarmass.

[0036] Bringing a block copolymer into solution in the PCM is made bysoftening of the polystyrene segments under the effect of temperature.The molecules are then free to move when shearing is applied. Thepolystyrene and the elastomer blocks are not compatible on thethermodynamic level. Accordingly the polystyrene segments at the end ofthe chain are grouped to form polystyrene domains. The elastomersegments form separate domains. Above a critical co-polymerconcentration, the tri-block rubbers form PCM gels with an elasticbehaviour (cohesive gels), whereas the di-block rubbers tend to form“greases”.

[0037] Under shearing, in the case of high mass polymers, themacromolecular coils are laminated with an orientation in the directionof flow and the thickening power is temporarily reduced. In the case ofionic polymers or block copolymers, shearing breaks the reversible bonds(ionic or physical), thus also inducing a temporary reduction inviscosity. This phenomenon may become more marked as the temperaturerises.

[0038] The consistency of a blocked convection phase change material(PCM-CB) as defined depends on:

[0039] the texturing agent concentration,

[0040] the type of polymer (plastic, elastomer, etc) or copolymerskeleton, molecular mass, flexibility, number of blocks etc.

[0041] the solvent capacity of the PCM in relation to the texturingagent (nature of the chains),

[0042] the dispersion forces,

[0043] and in addition in the case of charged polymers:

[0044] the faculty of the solvent (PCM) to ionise the ion pairs. Theless polar the solvent, the higher the interactions.

[0045] the proportion of charged groups, the nature of the ionic group(e.g. for anionic: carboxylate, sulfonate, phenate, salicylate,phosphonate), type of counter-ions (e.g. for anionic: cations: amine,metal, monovalent, multivalent, . . . ).

[0046] A suitable combination of these parameters will make it possibleto optimise the insulating power of the PCM-CB at temperatures higherthan the fusion temperature Tf of the PCM.

EXAMPLES OF COMPOSITIONS

[0047] Blocked convection PCMs can be formed by bringing into solution:

[0048] 1a) hydrocarbon polymers (apolar) such as polyisobutylenes orpolyisobutenes (PIB); ethylene, propylene or higher carbon polymers;ethylene, propylene or higher carbon copolymers and their derivatives;copolymers based on combined dienes (hydrogenated polybutadiene,hydrogenated butadiene-styrene, hydrogenated ethylene-butadiene andhydrogenated isoprene-styrene copolymers) linear, tri-block (e.g.styrene-ethylene-butadiene-styrene, grade G1651 from Kraton) or radial;or other styrene based polymers,

[0049] 1b) ester polymers (polar) such as alkyl polyacrylates; alkylpolymethacrylates; maleates and fumarates; itaconates;

[0050] 1c) mixed ester-hydrocarbon polymers such as olefin copolymersassociated with esters (OCP-esters); alkyl-styrene methacrylate oracrylate polymers; alkyl-αolefin or polyolefin acrylate or methacrylatecopolymers.

[0051] These polymers can be used alone or as a mixture (mixture ofpolyisobutene and hydrogenated diene-styrene, of olefin polymers orcopolymers, of hydrogenated dienes-styrene with ester polymers orcopolymers, etc) and can be functionalised by polar units such asimides, succimides, vinylpyrolidone, etc.

[0052] Blocked convection PCMs can also be formed by bringing intosolution ionomer polymers such as (generally, the ionic polymer isneutralised by a metallic or organometallic counter-ion):

[0053] 2a) anionic, cationic or amphoteric ionomers.

[0054] 2b) a combination of various ionomers.

[0055] 2c) telechelic polymers, i.e. the ionic groups are the chain ends(in this case, there are only two ionic groups per chain and themolecular mass is generally relatively low).

[0056] The ionic groups can be anionic (carboxylate, sulfonate,phosphonate, thioglyconate group), cationic (ammonium or pyridium salts,alkaline (Na, K) or alkaline-earth salts (Mg, Ca, Ba), amphoteric orzwitterionic (e.g. carboxylbetaine).

[0057] The main known industrial ionomers are those comprisingcarboxylate or sulfonate groups.

[0058] The following list is not limitative:

[0059] Carboxylated ionomers:

[0060] Ethylene and methacrylic acid copolymer;

[0061] Carboxylated elastomers: polymers consisting of monomerscontaining a carbolyxic acid (generally acrylic or methacrylic acid) andmonomers used for forming elastomers. These are for instance polymers ofstyrene-butadiene-acrylic acid, butadiene-acrylonitrile-acrylic acid,butadiene-acrylic acid polymers, . . . ;

[0062] Perfluorocarboxylated ionomers;

[0063] Sulfonated ionomers:

[0064] Sulfonated ethylene-propylene-diene terpolymers (sulfonatedEPDMs).

[0065] One preferred diene is 5-ethylidene-2-norbornene (ENB);

[0066] Sulfonated elastomers: polymers comprising sulfonated monomers(generally sulfonated styrene) and monomers used for forming elastomers.The sulfonated elastomers are derived from elastomer polymers chosenfrom the group formed of isoprene and sulfonated styrene copolymers,chloroprene and sulfonated styrene copolymers, isoprene and butadienecopolymers, styrene and sulfonated styrene copolymers, butadiene andsulfonated styrene copolymers, isoprene, styrene and sulfonated styreneterpolymers, butadiene, styrene and sulfonated styrene terpolymers,butyl rubber, partially hydrogenated polyisoprene, partiallyhydrogenated polybutylene, partially hydrogenated naturel rubber,partially hydrogenated polybutadiene, neoprene. The methods andcharacteristics of these sulfonated elastomers are known to the manskilled in the art (for instance, in documents U.S. Pat. No. 4,447,338,U.S. Pat. No. 4,425,462); p2 chlorosulfonated polyethylene;

[0067] perfluorosulfonated ionomers;

[0068] Telechelic ionomers: like carboxylated telechelic elastomers(e.g. butadiene and acrylonitrile copolymer functionalised at the twoends of the chain) or sulfonated telechelic elastomers based onpolyisobutylene.

[0069] The ionomer polymer can be added to the PCM at concentrationsvarying from 0.01 to 10%, and preferably 0.1 to 3% by mass with respectto the total mass.

Additives

[0070] To bring in certain specific properties, the following compoundscan advantageously be included in the compositions for someapplications.

1-Soluble Additives

[0071] a) Antioxidant additives may be added either duringimplementation, if the temperature is high (e.g.: Irganox 1010 fromCiba), or when the product (PCM with blocked convection) is exposed to atemperature rise in service. In this case, the most frequentlyencountered compounds are phenol derivatives (dibutylparacresol, etc.),phenol derivatives containing sulphur and aromatic amines (phenyl α or βnaphthylamine or alkyl amine diphenyls). These antioxidants slow downthe oxidation process because they inhibit the forming of free radicalsor have a destructive effect on the formed hydroperoxides.

[0072] b) antibacterial agents.

[0073] c) corrosion inhibitors:

[0074] c1) soluble in the liquid PCM, comprise polar chemical compoundswhich are adsorbed easily on the metallic surface while forming ahydrophobic film (fatty amines or amides and derived substances,alkaline-earth sulfonates, etc.);

[0075] c2) soluble in water and acting by passivation of the water phase(e.g., sodium nitrite).

2-Fillers

[0076] Insoluble fillers such as hollow glass microballs, fly ash,macroballs, hollow fibres, clayey compounds, etc, can be addedadvantageously to the PCM-CB to adjust its density and/or its thermalconductivity.

3-Solvents

[0077] To fluidify the blocked convection PCM, it is possible to usehydrocarbons of petroleum origin, such as hydrocarbon-containingsolvents: distillation cuts, predominantly aromatic, naphthenic orparaffinic oils obtained using solvent extraction processes or deephydro-treatment processes, solvents or cuts obtained byhydroisomerisation of paraffin extracts of petroleum origin, or byFischer Tropsch synthesis, solvents and compounds obtained by synthesis,for instance, oxygenated compounds of the ester type, synthetichydrocarbons such as hydrogenated polyolefins, etc. A PCM co-solvent canalso be used to check and adjust the influence of temperature on theviscosity.

[0078] The blocked convection PCM (PCM-CB) material typically comprisesbetween 60 and 99.99% liquid PCM and complementary texturing agent.Additives (<10%), fillers (5 to 60%), and solvents (0.2 to 20%) arepossibly added.

FORMULATION EXAMPLES

[0079] 1) In the case of an apolar PCM like a mixture of paraffins withviscosity of around 5 mPa.s at 40° C., a blocked convection formulationbased on this PCM, containing approximately 15% of a product based onhydrogenated butadiene-styrene (PBSH) and 0.5% of antioxidant agent, hasa viscosity of 100000 mPa.s at 40° C. This viscosity is reduced by 50%(50000 mPa.s) with shearing of 5 10⁵ s⁻¹ and by 70% (40000 mPa.s) withthe same shearing at 80° C.

[0080] 2) Gelation of 1 litre of liquid PCM is obtained by thedissolution of several ten grams/litre of a sulfonated ionomerneutralised by a zinc salt and having a sulfonate proportion of around30 millequivalent/100 g.

Applications

[0081] The blocked convection PCM materials described can be used, forinstance, for the thermal insulation of submarine lines.

[0082] In patent application FR 98/16.791 already mentioned, a thermalinsulation and device for submarine lines is described, intended to belaid on the seabed at a great depth. The device includes an outercoating consisting of a liquid/solid phase change material (PCM)quasi-incompressible having an intermediate fusion temperature betweenthe temperature of the effluents circulating in the line(s) and thetemperature of the outside medium, and an absorbing matrix surroundingthe lines as closely as possible. The lines and their coating are placedin a resistant and deformable protective sheath.

[0083] The outer coating consisting of the matrix impregnated with PCMdescribed in the prior document can be advantageously replaced by one ofthe blocked convection PCMs described above, having the result of animprovement in the thermal insulation of the lines and thesimplification of the installation operations around the line(s), forinstance, by pumping at a temperature higher than the fusion temperatureTf, particularly appreciable when the line assembly to be insulated iscomplex. Pumping is facilitated because, during shearing, the viscosityof the material decreases.

[0084] Applications of the material to thermal insulation of lines usedfor transporting fluids, especially hydrocarbons, have been described.It is obvious, however, that such a material can be used in any otherapplication requiring low thermal conductivity, combined with energyrelease.

1) Process for manufacturing a material based on phase change material(PCM), having low thermal conductivity, characterised in that itcomprises combination with a phase change material of a texturing agentchosen to greatly reduce the thermal convection at a temperature higherthan the fusion temperature of the phase change material and whosegelling or viscosifying capacity drops temporarily under shearing. 2)Process as claimed in claim 1, characterised in that it includes thecombination of a texturing agent in a solution in the phase changematerial. 3) Material based on phase change materials (PCM) exhibitinglow thermal conductivity at a temperature higher than the fusiontemperature of the phase change material, characterised in that itincludes in combination a phase change material (PCM) and a texturingagent chosen to greatly reduce the thermal convection at a temperaturehigher than the fusion temperature of the phase change material, andwhose gelling or viscosifying capacity drops temporarily under shearing.4) Material as claimed in claim 3, characterised in that it includes incombination a phase change material (PCM) and at least one, or mixturesthereof, of the polymers chosen from the group consisting of:non-dispersing or dispersing hydrocarbon polymers (apolar),non-dispersing or dispersing ester polymers (polar), or mixednon-dispersing or dispersing ester-hydrocarbon polymers. 5) Material asclaimed in claim 3, characterised in that it includes in combination aphase change material (PCM) and an ionomer texturing polymer defined asconsisting of macro molecules with a small percentage ofchemically-linked ionic groups distributed along non-ionic chains(skeletons). 6) Material as claimed in claim 5, characterised in thatthe texturing polymer referred to as the ionomer contains anionic groupssuch as: carboxylate, sulfonate, phenate, salicylate, phosphonate,thioglyconate), and/or cationic groups such as: ammonium, pyridium saltsor organometallic, alkaline or alkaline-earth salts and/or amphotericand/or zwitterionic groups such as carboxylbetaines. 7) Material asclaimed in any one of the previous claims, characterised in that itincludes 60 to 99.99% of liquid PCM, the complement consisting of atexturing agent, by mass. 8) Material as claimed in any one of claims 3to 7, characterised in that it includes in addition at least one solubleadditive acting as an anti-oxidant or anti-bacterial agent or acorrosion inhibitor. 9) Material as claimed in any one of claims 3 to 8,characterised in that it includes in addition at least one insolublefiller designed to adjust its density or is thermal conductivity. 10)Material as claimed in any one of claims 3 to 9, characterised in thatit includes in addition at least one solvent designed to control theviscosity. 11) Application of the material as claimed in any one ofclaims 3 to 10 to the thermal insulation of fluid carrying lines, inparticular for hydrocarbons, the product being used as line coating. 12)Application of the material as claimed in any one of claims 3 to 11 tothermal insulation of fluid carrying lines, in particular forhydrocarbons, the product being used as a coating for the lines andinterposed between the lines and an outer protective sheath. 13)Application of the material as claimed in any one of claims 3 to 12 tothe thermal insulation of fluid carrying lines, in particular forhydrocarbons, by injection of the material into the annulus between thelines and an outer protective sheath.